End-modified conjugated diene polymer and method for preparing the same

ABSTRACT

One aspect of the present invention provides an end-modified conjugated diene polymer represented by Formula 1 below: 
     
       
         
         
             
             
         
       
     
     wherein p is a conjugated diene polymer chain; R 1  to R 7  are each independently C 1 -C 20  saturated or unsaturated hydrocarbon chains; X is carbon (C), silicon (Si), or nitrogen (N); a is 1 or 2; and n is an integer of 1 to 200, and a method for preparing the same.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/933,595, filed Nov. 5, 2015, which claims the benefit under 35 U.S.C.§119 of Korean Patent Application No. 10-2014-0152678, filed Nov. 5,2014, which are hereby incorporated by reference in their entireties.

BACKGROUND Field of the Invention

The present invention relates to an end-modified conjugated dienepolymer and a method for preparing the same.

Discussion of Related Art

Recently, as the interest in eco-friendly and energy-saving highfunctional tires rises, the research on the development of highfunctional rubbers with dynamic properties such as rolling resistanceand wet resistance, mechanical properties, and machinability has beenconducted in various ways.

In general, styrene-butadiene rubbers (hereinafter, ‘SBR’) or butadienerubbers (hereinafter, ‘BR’) are used as rubbers for tires, and they aremainly manufactured by a solution polymerization method.

The solution polymerization method, which polymerizes a monomer amongsolvents using an organometallic compound as an initiator, tomanufacture rubbers, is capable of adjusting a structure of monomer orpolymer, a coupling rate, etc. The polymer manufactured according tosaid method has excellent rolling resistance and wet resistance, andthus said method is widely used for manufacturing rubbers for tires.

Additionally, according to the solution polymerization method, the coldflow at room temperature can be controlled by introducing a functionalgroup into a part of polymer using a modifying agent, and machinabilityand dispersibility can be improved when combined with a reinforcingagent. Especially, dynamic properties of tires, such as wear resistance,rolling resistance, wet resistance, etc., may be improved by increasingcompatibility with carbon black or silica, which is a reinforcing agentused, when combined in a rubber composition for tires.

According to U.S. Pat. No. 5,508,333, more excellent dynamic propertiesand mechanical properties may be acquired than the conventional rubberhas by modifying molecular ends to alkoxysilane compounds including anepoxy group. However, it is difficult to control the coupling rate.

According to US Patent Publication No. 2010-0152369, the use ofalkoxysilane compounds including primary amine substituted withhydrolysable protective groups as end modifying agents may reducehysteresis of the tire manufactured therefrom. However, in this case,there is an economical limit resulting from the application ofprotective groups. Additionally, the cold flow is high, and accordingly,long-term storage stability may be reduced.

Thus, it is necessary to develop a conjugated diene polymer for tirerubber capable of increasing compatibility or miscibility with thereinforcing agents through end modification, and also improvingmechanical and dynamic properties of the tire manufactured therefrom.

BRIEF SUMMARY

The present invention aims to solve the problems stated above. Thepurpose of the present invention is to provide an end-modifiedconjugated diene polymer capable of increasing compatibility ormiscibility with reinforcing agents such as silica or carbon black, andimproving mechanical and dynamic properties of tire, which is a finalproduct, and a method for preparing the same.

In order to achieve the above purpose, one aspect of the presentinvention provides an end-modified conjugated diene polymer representedby Formula 1 below:

In the Formula 1, p is a conjugated diene polymer chain, R¹ to R⁷respectively are each C₁-C₂₀ saturated or unsaturated hydrocarbonchains; X is carbon (C), silicon (Si), or nitrogen (N); a is 1 or 2; andn is an integer of 1 to 200.

According to one embodiment of the present invention, the conjugateddiene polymer chain may be a (homo) polymer chain including a conjugateddiene monomer.

According to one embodiment of the present invention, the polymer chainmay be a copolymer chain further including an aromatic vinyl monomer.

Additionally, another aspect of the present invention provides a rubbercomposition for tires, including the end-modified conjugated dienepolymer.

According to one embodiment of the present invention, the compositionhas a Mooney viscosity of 40 to 150.

According to one embodiment of the present invention, the compositionhas a Mooney viscosity of 40 to 100.

According to one embodiment of the present invention, the compositionhas a Mooney viscosity of 80 to 100.

Additionally, yet another aspect of the present invention provides amethod for preparing an end-modified conjugated diene polymer, whichincludes the steps of (a) polymerizing at least one monomer of aconjugated diene monomer and an aromatic vinyl monomer to form a livingpolymer in the presence of a solvent, a lewis base, and anorganometallic compound; and (b) reacting the living polymer with acompound represented by Formula 2 below:

to modify an end of the living polymer.

In the Formula 2, R¹ to R⁸ are each C₁-C₂₀ saturated or unsaturatedhydrocarbon chains; X is carbon (C), silicon (Si), or nitrogen (N); a is1 or 2; b, c and d are each integers of 0 to 3 satisfying an equation ofb+c+d=3, and n is an integer of 1 to 200.

According to one embodiment of the present invention, the organometalliccompound may be used in an amount of 0.01 mmol to 10 mmol with respectto 100 g of the monomer.

According to one embodiment of the present invention, the organometalliccompound may be at least one selected from the group consisting of anorganolithium compound, an organosodium compound, an organopotassiumcompound, an organorubidium compound, and an organocesium compound.

According to one embodiment of the present invention, a molar ratio ofthe organometallic compound and the compound represented by Formula 2may be 1:0.5 to 1:3.0.

An end-modified conjugated diene polymer according to one aspect of thepresent invention allows at least one alkoxysilane group introducedbetween the ends of main chains or between main chains to easily controla coupling rate and cold flow, thereby improving long-term storagestability. Additionally, at least one nitrogen atom introduced together,that is, tertiary amine-based component, increases binding force betweenpolymers and reinforcing agents when combined in rubber compositions,thereby improving dynamic properties such as wet resistance, rollingresistance, etc., and mechanical properties of the final product tires.

The present invention is not limited to the above-mentioned effects.Additionally, it should be understood that the present inventionincludes all effects which can be inferred from the constitutionsdescribed in the detailed description or the claims.

DETAILED DESCRIPTION

Hereinafter, the present invention will be explained with reference tothe accompanying drawings. The present invention, however, may bemodified in various different ways, and should not be construed aslimited to the embodiments set forth herein. Also, in order to clearlyexplain the present invention, portions that are not related to theexplanation are omitted from the drawings, and like reference numeralsare used to refer to like elements throughout.

Throughout the specification, it will be understood that when a portion“includes” an element, unless specifically described to the contrary, itshould be understood that the portion does not exclude another elementbut may further include another element.

The embodiments of the present invention will be explained in detailwith reference to the drawings attached.

An End-Modified Conjugated Diene Polymer

One aspect of the present invention provides an end-modified conjugateddiene polymer represented by Formula 1 below:

In the Formula 1, p is a conjugated diene polymer chain, R¹ to R⁷ areeach C₁-C₂₀ saturated or unsaturated hydrocarbon chains; X is carbon(C), silicon (Si), or nitrogen (N); a is 1 or 2; and n is an integer of1 to 200.

Especially, when a is 1 in the Formula 1, since X has a sp³ hybridstructure, and nitrogen atoms are respectively introduced to twobranches extended from one X to form at least two tertiary amine groups,the conjugated diene polymer may be adjacent to silica by a hydrogenbond between silica, which is a reinforcing agent, and the amine groupwhen combined in the rubber composition. At this time, a covalent bondmay be formed between the alkoxysilane group of conjugated diene polymerand silica. The hydrogen bond and covalent bond reinforce a chemicalbond between the conjugated diene polymer and silica, thereby improvingdynamic properties, such as wet resistance, rolling resistance, etc.,and mechanical properties required for tires.

Referring to the Formula 1, the polymer according to one aspect may beobtained by polymerizing a conjugated diene monomer alone, or modifyingthe end of a main chain where a conjugated diene monomer and an aromaticvinyl monomer are copolymerized by an alkoxysilane compound.

The conjugated diene monomer may be at least one selected from the groupconsisting of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene,1,3-pentadiene, 1,3-hexadiene, 2,3-dimethylbutadiene,2-phenyl-1,3-butadiene, 3-methyl-1,3-pentadiene, 2-chloro-1,3-butadiene,piperylene, 3-butyl-1,3-octadien, and octadien. Preferably, theconjugated diene monomer may be 1,3-butadiene, isoprene, or2,3-dimethyl-1,3-butadiene, but is not limited thereto.

The aromatic vinyl monomer may be at least one selected from the groupconsisting of styrene, α-methylstyrene, 2-methylstyrene,3-methylstyrene, 4-methylstyrene, 2,4-dimethylstyrene,2,4-diisopropylstyrene, 4-propylstyrene, 4-cyclohexylstyrene,4-(p-methylphenyl)styrene, 5-tert-butyl-2-methylstyrene,tert-butoxystyrene, 2-tert-butylstyrene, 3-tert-butylstyrene,4-tert-butyl styrene, N,N-dimethylaminoethylstyrene,1-vinyl-5-hexylnaphthalene, 1-vinylnaphthalene, divinylnaphthalene,divinylbenzene, trivinylbenzene, vinylbenzyldimethylamine,(4-vinylbenzene)dimethylaminoethylether, vinylpyridine, vinylxylene,vinyltoluene, diphenylethylene, diphenylethylene including tertiaryamine, and styrene including primary, secondary, or tertiary amine.Preferably, the aromatic vinyl monomer may be styrene orα-methylstyrene, but is not limited thereto.

Additionally, when the conjugated diene polymer chain includes aconjugated diene monomer and an aromatic vinyl monomer, a weight ratioof the conjugated diene monomer to aromatic vinyl monomer may be 55% to95% by weight : 5% to 45% by weight. When the content of aromatic vinylmonomer in the conjugated diene polymer chain is within the above range,a glass transition temperature (Tg) of copolymer increases. Thus, whenapplying to tires, physical properties, such as wet resistance, rollingresistance, or braking force, required for tires may be satisfied, andfuel efficiency may also be improved.

Additionally, another aspect of the present invention provides a rubbercomposition for tires including the end-modified conjugated dienepolymer. The rubber composition for tires may further includereinforcing agents such as silica and carbonblack.

In general, in case of preparing a rubber composition for tires bycombining a polymer with a reinforcing agent, the viscosity of therubber composition increases while the combination of the polymer andthe reinforcing agent progresses. The increase of viscosity may impedeworkability, storability and machinability of the rubber compositionwhen manufacturing tires, so it is important to control the viscosity ata proper level. Specifically, when a Mooney viscosity of the rubbercomposition for tires exceeds 150, this may impede workability,storability and machinability. Thus, the Mooney viscosity of the rubbercomposition for tires may be adjusted in the range of 40 to 150,preferably in the range of 40 to 100, more preferably in the range of 80to 100 by using the end-modified conjugated diene polymer.

A Method for Preparing an End-Modified Conjugated Diene Polymer

Another aspect of the present invention provides a method for preparingan end-modified conjugated diene polymer, which includes the steps of(a) polymerizing at least one monomer of a conjugated diene monomer andan aromatic vinyl monomer to form a living polymer in the presence of asolvent, a lewis base, and an organometallic compound; and (b) reactingthe living polymer with a compound represented by Formula 2 below:

to modify an end of the living polymer.

In the Formula 2, R¹ to R⁸ are each C₁-C₂₀ saturated or unsaturatedhydrocarbon chains; X is carbon (C), silicon (Si), or nitrogen (N); a is1 or 2; b, c and d are each integers of 0 to 3 satisfying an equation ofb+c+d=3, and n is an integer of 1 to 200.

The step (a) forms a living polymer according to a general solutionpolymerization method. Specifically, the step (a) is performed in thepresence of a solvent, a lewis base and an organometallic compound, andmay use, as a monomer, a conjugated diene monomer alone, or a mixture ofa conjugated diene monomer and an aromatic vinyl monomer.

The conjugated diene monomer may be at least one selected from the groupconsisting of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene,1,3-pentadiene, 1,3-hexadiene, 2,3-dimethylbutadene,2-phenyl-1,3-butadiene, 3-methyl-1,3-pentadiene, 2-chloro-1,3-butadiene,piperylene, 3-butyl-1,3-octadien, and octadien. Preferably, theconjugated diene monomer may be 1,3-butadiene, isoprene, or2,3-dimethyl-1,3-butadiene, but is not limited thereto. The aromaticvinyl monomer may be at least one selected from the group consisting ofstyrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene,4-methylstyrene, 2,4-dimethylstyrene, 2,4-diisopropylstyrene,4-propylstyrene, 4-cyclohexylstyrene, 4-(p-methylphenyl)styrene,5-tert-butyl-2-methylstyrene, tert-butoxystyrene, 2-tert-butylstyrene,3-tert-butylstyrene, 4-tert-butylstyrene, N,N-dimethylaminoethylstyrene,1-vinyl-5-hexylnaphthalene, 1-vinylnaphthalene, divinylnaphthalene,divinylbenzene, trivinylbenzene, vinylbenzyldimethylamine,(4-vinylbenzene)dimethylaminoethylether, vinylpyridine, vinylxylene,vinyltoluene, diphenylethylene, diphenylethylene including tertiaryamine, and styrene including primary, secondary, or tertiary amine.Preferably, the aromatic vinyl monomer may be styrene orα-methylstyrene, but is not limited thereto. Additionally, when theconjugated diene polymer chain includes a conjugated diene monomer andan aromatic vinyl monomer, a weight ratio of the conjugated dienemonomer to the aromatic vinyl monomer may be 55% to 95% by weight: 5% to45% by weight.

A solvent available when polymerizing the solution may be one selectedfrom the group consisting of aliphatic hydrocarbons, alicyclichydrocarbons, aromatic hydrocarbons, and a combination of at least twothereof. Preferably, the solvent may be one selected from the groupconsisting of n-pentane, n-hexane, n-heptane, isooctane, cyclohexane,toluene, benzene, xylene, and a combination of at least two thereof, andmore preferably, may be cyclohexane, but is not limited thereto. Themonomers may be included in an amount of 5% to 40% by weight,preferably, 10% to 25% by weight in the solvent. When the content ofmonomer in the solvent is less than 5% by weight, a great deal ofsolvent may be used, and accordingly, manufacturing yield may be reducedand production cost may be increased. When the content of monomerexceeds 40% by weight, it may be difficult to control viscosity and heatof reaction of the polymerization solution.

The lewis base, which is a material used to control a microstructure ofa polymer, may be one selected from the group consisting oftetrahydrofuran, di-n-propyl ether, diisopropylether, diethylether,diethyleneglycol dimethyl ether, di-n-butyl ether, ethyl butyl ether,triethylene glycol, 1,2-dimethoxybenzene, ditetrahydrofurylpropane,ditetrahydrofurfurylpropane, ethyltetrahydrofurfuryl ether,trimethylamine, triethylamine, N,N,N,N-tetramethylethylenediamine, and acombination of at least two thereof. Preferably, the lewis base may beethyltetrahydrofurfuryl ether, tetrahydrofuran,ditetrahydrofurfurylpropane, ditetrahydrofurylpropane, orN,N,N,N-tetramethylethylenediamine, but is not limited thereto. Theamount of the lewis base to be introduced may be adjusted according tothe number of mol in a total of anions, and the content of vinyl in thetarget conjugated diene compound at an initial temperature condition.

The organometallic compound serving as a polymerization initiator in thestep (a) may be at least one selected from the group consisting of anorganolithium compound, an organosodium compound, an organopotassiumcompound, an organorubidium compound, and an organocesium compound,preferably, may be an organolithium compound, and more preferably, maybe an alkyl lithium compound having an alkyl group with 1-20 carbonatoms. The alkyl lithium compound available may be one selected from thegroup consisting of methyllithium, ethyllithium, isopropyllithium,n-butyllithium, sec-butyllithium, tert-butyllithium, and a combinationof at least two thereof, and preferably, may be n-butyllithium orsec-butyllithium, but is not limited thereto. The usage of theorganometallic compound may vary depending on a target molecular weightof a polymer generated, but generally, 0.01 mmol to 10 mmol, preferably,0.1 mmol to 3.0 mmol of organometallic compound may be used with respectto 100 g of a monomer.

The onset temperature of polymerization during solution polymerizationin the step (a) may be about 10° C. to 100° C., preferably, about 20° C.to 90° C. When the onset temperature is less than 10° C., the viscosityof the solution rapidly increases as the reaction proceeds, andaccordingly, the reaction rate may be decreased, which isdisadvantageous economically. When the onset temperature exceeds 100°C., it may be difficult to control the reaction temperature.Additionally, the reaction pressure may be 0.5 kgf/cm² to 10 kgf/cm². Ingeneral, the polymerization may be performed for a sufficient time untilall of the monomers are converted into copolymers, that is, for 20 to200 minutes until a target conversion rate is achieved.

Secondly, the step (b) reacts the living polymer formed in the step (a)with the alkoxysilane compound represented by the Formula 2 to modifythe end of the living polymer.

The alkoxysilane compound represented by the Formula 2 may bemanufactured with a route of Scheme 1 or 2 below depending on the typeof atom X. In the Scheme 1 or 2 below, R¹ to R⁸ are each C₁-C₂₀saturated or unsaturated hydrocarbon chains; X is carbon (C), silicon(Si), or nitrogen (N); L is an optional leaving group; a is 1 or 2; b, cand d are each integers of 0 to 3 satisfying an equation of b+c+d=3; andn is an integer of 1 to 200.

First of all, when the atom X is nitrogen, the alkoxysilane compoundaccording to one embodiment may be manufactured by nucleophilicsubstitution represented by the Scheme 1 above in the presence of abase. At this time, the reaction temperature may be adjusted in therange of −30° C. to 150° C. As the base, hydride, hydroxide, carbonate,or bicarbonate of alkali metal or alkali earth metal may be used, andspecifically, sodium hydride (NaH) or sodium hydroxide (NaOH) may beused. As the reaction solvent, polar organic solvents capable ofincreasing solubility of a reactant, for example, dimethylformaldehydemay be used.

Additionally, when the atom X is carbon or silicon and thus cannot actas a nucleophilic agent, that is, nucleophilic substitution cannot beperformed, an alkoxysilane compound according to one embodiment may bemanufactured by a hydrosilylation reaction represented by the Scheme 2in the presence of platinum (Pt). At this time, the reaction temperaturemay be a reflux temperature, and this may vary depending on the type ofreaction solvent used. However, the reaction temperature may be adjustedin the range of about 100° C. to 180° C. The type of reaction solvent isnot particularly limited, but it is preferable to use aromatic solventssuch as benzene and toluene.

Meanwhile, the alkoxysilane compound represented by the Formula 2 may beused in the range of 0.5 mol to 3.0 mol per 1 mol of the organometalliccompound. When a relative usage for 1 mol of the organometallic compoundis less than 0.5 mol, an effect of modifying an end of the livingpolymer may be slight. When the relative usage exceeds 3.0 mol, a greatdeal of modifying agents are used, and accordingly, manufacturing yieldmay be reduced and production cost may be increased.

Additionally, while modifying the end in the step (b), the reactiontemperature may be between 30° C. and 200° C., preferably, between 50°C. and 110° C. When the reaction temperature is less than 30° C., theviscosity of the solution increases as the reaction proceeds, and thusthe reaction rate may be decreased. When the reaction temperatureexceeds 200° C., the living polymer performs a coupling reaction byitself, and thus an effect of modifying the end by the alkoxysilanecompound may be slight.

Hereinafter, the present invention will be explained in detail withreference to the embodiments. Meanwhile, the embodiments are for theillustrative purposes only, and the contents of the present inventionare not limited thereto.

EXAMPLE 1

22 g of styrene, 369 g of 1,3-butadiene, 2,200 g of normal heptane, and5 mL of ethyltetrahydrofurfuryl ether were put into a 5 L reactor, andwhile stirring, a temperature inside the reactor was adjusted to 35° C.When the temperature inside the reactor reaches 35° C., 1.7 mmol ofn-butyllithium, which is a polymerization initiator, was added andadiabatic temperature-rising polymerization was performed. At this time,progression of the polymerization was observed through the change inreaction temperature. Additionally, the rate of monomer and theconversion rate of reaction were analyzed by sampling a small quantityof reactants between the reactions.

When the polymer conversion rate of the monomer reaches 99%, additional9 g of 1,3-butadiene was added to substitute the reaction end withbutadiene. Afterwards, 2.7 mmol ofN¹,N¹-diethyl-N²,N²-bis(3-(trimethoxysilyl)propyl)ethane-1,2-diamine,which is an end modifying agent, was added to the reactor and left for acertain time, and then 4 g of butylated hydroxy toluene (BHT), which isan antioxidant, was added to terminate the reaction. After that,stripping and roll-drying were performed to remove the residual solventand water, and a polymer was obtained.

EXAMPLE 2

A polymer was obtained in the same manner as Example 1 above, exceptthat 2.7 mmol of 6-(2-(dimethylamino)ethyl)-N¹,N¹,N²⁰,N²⁰-tetramethyl-3-(3-trimethoxysilyl)propyl)decane-1,10-diamine was addedas an end modifying agent.

COMPARATIVE EXAMPLE 1

A polymer was obtained in the same manner as Example 1 above, exceptthat an end modifying agent was not added.

COMPARATIVE EXAMPLE 2

A polymer was obtained in the same manner as the Example 1 above, exceptthat 2.7 mmol of N,N-dimethylaminopropyltrimethoxysilane was added as anend modifying agent.

Table 1 below shows properties of end-modified copolymers manufacturedin the Examples 1 and 2, and in Comparative Examples 1 and 2. In theTable 1 below, the end modification rate, styrene content, and vinylcontent are mol % values calculated by using NMR analysis result values,and weight-average molecular weight was measured through gel permeationchromatography (GPC).

TABLE 1 Weight- average Mooney Vinyl End molecular viscosity Styrenecontent in modification weight (ML₁₊₄, content BD unit rate (mol %) (Mw)100° C.) (mol %) (mol %) Example 1 58 546,000 73 10.1 39.8 Example 2 42512,000 70 10.0 39.7 Comparative 0 215,000 41 9.9 39.8 Example 1Comparative 29 490,000 72 10.0 40.0 Example 2

Experimental Example Evaluation on Properties of Rubber Composition forTire

Each copolymer manufactured according to Examples 1 and 2, andComparative Examples 1 and 2 above was combined with silica in a 500 cclab mixer according to conditions shown in Table 2 below to manufacturea rubber composition for tires.

TABLE 2 Components of composition Content (phr) Solution SBR 80 High cisBR 20 Stearic acid 2 ZnO₂ 3 Silica 80 Aromatic oil 10 Si-69 6.4 CZ 1 DPG1.5 sulfur 1.5 Solution SBR: Copolymer obtained in Examples 1 and 2, andComparative Examples 1 and 2 High cis BR: KBR01 (Kumho PetrochemicalCo., Ltd.) Si-69: bis-(triethoxysilylpropyl)tetra-surfide CZ:N-cyclohexylbenzothiazyl sulfonamide DPG: 1,3-diphenylguanidine

Machinability of the rubber compositions and properties thereof aftercombination were measured and compared, and the result thereof is shownin Table 3 below. The method for measuring the properties is as below.

-   -   Hardness: Measured by using a SHORE-A hardness tester    -   Tensile strength, 300% modulus and elongation percentage:        Measured by using a universal test machine (UTM) based on ASTM        3189 Method B.    -   Tanδ, which is a dynamic property value of vulcanized rubber:        Analyzed in a modification condition of frequency 10 Hz, 0.2 by        using Rheometic's DTMA 5 equipment.

TABLE 3 Comparative Comparative Properties Evaluation Item Example 1Example 2 Example 1 Example 2 Mechanical Hardness 71 70 65 69 properties(SHORE-A) Tensile 172 161 121 160 strength (kgf/cm²) 300% modulus 168151 — 149 (kgf/cm²) Elongation 373 364 260 360 percentage (%) Boundrubber 56 51 17 31 (wt %) Dynamic Tg (° C.) −48.8 −48.0 −48.0 −48.1properties Tanδ at 0° C. 0.2195 0.1914 0.1103 0.1354 (wet resistance)Tanδ at 60° C. 0.0781 0.0810 0.10018 0.0991 (rolling resistance)Machinability/ Mooney 84 92 149 105 Storability viscosity Cold flow 0.910.94 2.1 1.9 (mg/min)

Referring to Table 3 above, first of all, the rubber composition wherethe copolymers of Examples 1 and 2 are combined has a lower Mooneyviscosity and cold flow than the copolymers of Comparative Examples 1and 2. Thus, it can be known that machinability and storage stabilityare improved. Especially, the rubber compositions of Examples 1 and 2have low cold flow, so they may maintain their original package shapewhen packaging a certain standard, regardless of the weight, pressureand time. Thus, the rubber compositions in Examples 1 and 2 may beadvantageous for consumers producing and manufacturing other productsusing the composition.

Additionally, it was confirmed that the hardness, tensile strength, 300%modulus and elongation percentage of the rubber compositions in whichthe copolymers of Examples 1 and 2 are combined are partially improvedcompared to those of Comparative Examples 1 and 2. Especially, thecontent of bound rubber in the rubber compositions increases by about70% to 200%, and thereby binding force between the copolymer and silicais greatly reinforced.

Furthermore, when comparing tans values at 0° C. and 60° C. between theExamples and Comparative Examples, the rubber compositions where thecopolymers of Examples 1 and 2 are combined have high wet resistance (0°C.) and lower rolling resistance (60° C.). Thus, it can be understoodthat the tire to which the rubber compositions of Examples 1 and 2 applyhas improved stability and fuel efficiency.

Although the forgoing description of the present invention has beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the presentinvention as disclosed in the accompanying claims. Therefore, it shouldbe understood that the embodiments described above are by way of exampleonly, and are not intended to limit the present invention. For example,each constituent explained in singular form may be carried out beingdispersed, and likewise, constituents explained as being dispersed maybe carried out in combined forms.

The scope of the present invention is defined by the following claims,and it should be construed that the present invention covers themodifications or variations of the present invention provided they comewithin the scope of the appended claims and their equivalents.

What is claimed is:
 1. A method for preparing an end-modified conjugateddiene polymer, comprising: (a) polymerizing at least one monomer of aconjugated diene monomer and an aromatic vinyl monomer to form a livingpolymer in the presence of a solvent, a lewis base, and anorganometallic compound; and (b) reacting the living polymer with acompound represented by Formula 2 below:

to modify an end of the living polymer, wherein R¹ to R⁸ are each C₁-C₂₀saturated or unsaturated hydrocarbon chains; X is carbon (C), silicon(Si), or nitrogen (N); a is 1; b, c and d are each integers of 0 to 3satisfying an equation of b+c+d=3; and n is an integer of 1 to
 200. 2.The method of claim 1, wherein the organometallic compound is used in anamount of 0.01 mmol to 10 mmol with respect to 100 g of the monomer. 3.The method of claim 2, wherein the organometallic compound is at leastone selected from the group consisting of an organolithium compound, anorganosodium compound, an organopotassium compound, an organorubidiumcompound, and an organocesium compound.
 4. The method of claim 2,wherein a molar ratio of the organometallic compound to the compoundrepresented by the Formula 2 above is 1:0.5 to 1:3.0.